This disclosure will be particularly discussed in relation to stent grafts for placement into the thoraco-abdominal aorta for the treatment of aneurysms and more specifically in relation to placement in a curved portion of the aorta such as the thoracic arch. The disclosure, however, is not so restricted and may be applied to stent grafts for placement in any lumen of the human or animal body.
A stent graft is in a constricted form when it is delivered by endoluminal techniques to a deployment site within such a curved portion of the aorta. There have been devised diameter reducing arrangements for stent grafts so that there is a partial release stage of the stent graft after a covering sheath has been withdrawn. At this stage, the stent graft has expanded in diameter to such an extent that the physician can visualise using radiographic techniques the position of the stent graft, while at the same time the stent graft can still be rotated and moved longitudinally to position the stent graft correctly. The diameter reducing arrangements can be subsequently released to allow the stent graft to fully expand engage the wall of the vessel to form an alternative flow path through the vessel to bypass an aneurysm, for instance.
The problem with a curved lumen with significant continuing blood flow and such a staged release arrangement is that the proximal or leading edge of the stent graft particularly at the inner side of the curved lumen may not engage against the wall of the lumen and may fold in thereby blocking the desired flow path and allowing bypass to continue into the aneurysm. It is also important that a strent graft take up the curvature of a vessel into which it is placed.
It is an object of this disclosure to provide a diameter reducing arrangement so that this problem can be reduced or to at least to provide a physician with an alternative arrangement.
Throughout this specification the term distal with respect to a portion of the aorta, a deployment device or a prosthesis means the end of the aorta, deployment device or prosthesis further away in the direction of blood flow away from the heart and the term proximal means the portion of the aorta, deployment device or end of the prosthesis nearer to the heart. When applied to other vessels similar terms such as caudal and cranial should be understood.